Method for determining a state of a road during the driving mode of a motor vehicle

Abstract

In a method for determining the state of a road during driving of a motor vehicle, the sound which is generated when a vehicle tire rolls on an underlying surface is sensed. A frequency signal is determined by means of a sound level signal which describes the sound, and is divided into at least two sub-zones by means of at least one limiting frequency. The sub-zones are each assigned to an associated frequency band, and an intensity value is determined for each of at least two frequency bands from the assigned sub-zone of the frequency signal. The intensity value is characteristic of the sound intensity which is present in a frequency band. An intensity ratio is formed from two intensity values by dividing the first intensity value of the first frequency band by the second intensity value of the second frequency band, and is used to determine the state of a road.

1. A method for determining the state of a road during driving of a motor vehicle, comprising:
 sensing at least a portion of a sound generated when a vehicle tire rolls on an underlying road surface being sensed;  
 generating a sound level signal which describes said sound, using said at least a portion; and  
 determining a frequency signal which characterizes the sound level signal; wherein  
 the frequency signal is divided, by means of at least one limiting frequency, into at least two sub-zones which are each assigned to an associated frequency band;  
 an intensity value is determined for each of at least two frequency bands from the assigned sub-zone of the frequency signal, said intensity value being characteristic of the sound intensity present in a frequency band;  
 an intensity ratio is formed by dividing a first intensity value of a first frequency band by a second intensity value of a second frequency band; and  
 the intensity ratio is used to determine the state of the road.  
 
     
     
       2. The method as claimed in  claim 1 , wherein the frequency signal is determined on the basis of a chronologically limited section of the sound level signal. 
     
     
       3. The method as claimed in  claim 1 , wherein to determine the state of the road,
 at least one determined intensity ratio is compared with a predefinable value range assigned to a road state; and  
 the actual state of the road is determined based on this comparison.  
 
     
     
       4. The method as claimed in  claim 1 , wherein the frequency signal comprises a spectrogram. 
     
     
       5. The method as claimed in  claim 1 , wherein
 a quadratic matrix is determined for a frequency band, a matrix element being characteristic of the intensity of the sensed sound level signal within a predefinable frequency sub-band and within a predefinable time subsection; and  
 the norm of the matrix is determined as an intensity value.  
 
     
     
       6. The method as claimed in  claim 5 , wherein the matrix has 2 k  rows and 2 k  columns, k being an integer. 
     
     
       7. The method as claimed in  claim 1 , wherein intensity ratios are determined for each pair of adjacent frequency bands and used to determine the road state. 
     
     
       8. The method as claimed in  claim 1 , wherein each of the frequency bands has the same bandwidth. 
     
     
       9. The method as claimed in  claim 1 , wherein at least one of thickness of a film of water on the underlying surface, presence of snow or ice on the underlying surface and type of covering of the underlying surface is determined as a road state. 
     
     
       10. The method as claimed in  claim 1 , wherein a maximum possible coefficient of friction between the underlying surface and the vehicle tires is determined as a road state.